From the article "Some Myths about Marihuana" written by Dr. J.D Reichard (Medical Director, United States Public Health Service

Belief in such action seems to have originated in what was thought to have been the practice among the Assassins, a sect with strongholds in Persia and Syria during the Ilth, 12th, and 13th centuries of this era. This organization was an early form of "Murder, Inc." The head of the sect, called by Europeans "The Old Man of the Mountains," was reported to intoxicate his devotees with hashish, a derivative of the hemp plant, as a reward for having successfully carried out a homicidal mission. This substance was supposed to produce vivid sexual hallucinations. Let us look at the records.

Marco Polo, who visited these regions about 30 years after the Old Man of the Mountains and his sect were liquidated by the Tartars, reported on the Assassins as follows:[9] Young men of the community, whom the "Master" wished to recruit to his organization were rendered unconscious by opium, and then carried into a garden inhabited by numbers of beautiful, agreeable, and complaisant girls. Here they were permitted to regain consciousness. After several days of the companionship of the young ladies, the young men were again rendered unconscious by opium and removed from the garden. When interviewed by the "Master" they reported that they had been in Paradise. They were told: "He who defends his lord shall inherit Paradise." Polo states that "they were then forward to die in his service." Alas for the myth; there was no hashish and the ladies were quite real.

The force of a well established myth can be seen in the edition of Polo' travels referred to. In a foot-note only 2 pages after Polo's clear and unequivocal statement, the editor identifies hashish as the substance used to "intoxicate the young men."

[9] The Travda of Marco Polo (The Kublai Khan Edition). New York: Horace Liveright, 1930.